Method for Monitoring an Electrochemical Treatment Process and Electrode Arrangement Suited for Carrying Out This Method

ABSTRACT

There is described a counter-electrode arrangement that, e.g. can be used when coating and removing coatings from turbine blades, and to a method for the operation thereof. The counter-electrode arrangement comprises a reference electrode arrangement that is connected to the counter-electrode in an electrically non-conductive manner via contact elements. During the treatment process, a balanced potential over the surface to be treated is created by adapting the reference electrode arrangement, which as individual electrodes, to a surface to be treated. In a method for operating the counter-electrode arrangement, a measuring current can be applied to this arrangement in a first step for creating a balanced potential. The individual electrodes of the reference electrode arrangement can be separately contacted in order to determine the respective local potential on the surface of the component to be treated. The counter-electrodes can be adjusted so that a balanced potential prevails on the individual electrodes. During the subsequent treatment of the workpiece, the individual electrodes are interconnected in parallel and used as a reference electrode for maintaining a required treatment potential.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2005/056005, filed Nov. 16, 2005 and claims the benefit thereof. The International Application claims the benefits of German application No. 10 2004 056 158.3 DE filed Nov. 17, 2004, both of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a method for monitoring an electrochemical treatment process for a workpiece forming a working electrode, in which a predetermined potential between working electrode and the counter-electrode arrangement is maintained using a reference electrode arrangement.

BACKGROUND OF INVENTION

Methods of this type are generally known. For example EP 639 769 A2 discloses a method in which a defined potential is applied between a working electrode and a counter-electrode, with this potential being maintained during the electrochemical treatment process by means of a reference electrode. For this purpose the working electrode, the counter-electrode and the reference electrode are connected to a potentiostat.

SUMMARY OF INVENTION

An object of invention is to specify a method for monitoring an electrochemical treatment process, with the aid of which this treatment process can be controlled comparatively precisely based on the desired treatment result.

This object is inventively achieved by the method given at the start of this document by the reference electrode arrangement featuring a number of individual electrodes which are guided at a number of locations in a non-contact fashion to the surface of the workpiece to be treated. The use of a reference electrode arrangement with a number of individual electrodes advantageously ensures that a locally-resolved measurement can be undertaken as regards the workpiece surface regarding the setting of the predetermined potential. The measured values created by the individual electrodes can then be taken into account in setting the predetermined potential. In this case the measurement results of the individual electrodes can be considered separately or it is possible to consider all electrodes together. The measured values determined by means of the reference electrode arrangement can further be used to optimize the interaction of the workpiece with the counter-electrode arrangement. In this case for example distances or also the shaping of the counter-electrode arrangement can be modified, for example to accommodate non-planar workpiece geometries in respect of a uniform electrochemical treatment result.

All electrochemical methods are to be understood as electrochemical treatment processes in the sense of the invention. Such processes can typically involve the electrochemical removal of layers, the electrochemical dissolving of layers (decoating or stripping), electrochemical polishing (surface treatment) or also an electrochemical shaping (e.g. drilling).

In accordance with a further development of the invention there is provision for a voltage to be applied to the workpiece and to the counter-electrode arrangement before the electrochemical treatment which creates a low measurement current by comparison with the treatment process current, and for comparison potentials to be determined in each case at the individual electrodes of electrodes combined into a number of groups of the reference electrode arrangement. The measurement result created can thus be resolved in the way specified above in respect of the position on the surface of the component to be treated. Since only a small measurement current is used, the measurement result is only affected slightly by the processes normally executing in electrochemical treatment. Thus the measurement result created can for example be used for an exact positioning of the counter-electrode with complex workpiece geometries. Furthermore regions of the workpiece can be detected which may be problematic for carrying out the electrochemical treatment process. These can for example be taken into account by adapting the geometry of the counter-electrode arrangement (e.g. measures for modifying the local process-related current density of the process current at these points). In non-problematic areas of the workpiece the individual electrodes of the reference electrode arrangement can also be combined electrically into a group, so that these create a joint measured value.

In order to achieve an especially even electrochemical treatment of the workpiece surface, the reference electrode arrangement can be used to arrange the counter-electrode arrangement in relation to the workpiece such that the comparison potentials of the relevant individual electrodes are balanced as far as possible. If the electrochemical treatment process is then started, a comparatively balanced current density is achieved with a counter-electrode arrangement aligned in this way over the surface of the workpiece, which advantageously enables an even treatment result to be achieved.

Furthermore the inventive method can be used to apply the potential predetermined for the process to the workpiece and to the counter-electrode arrangement, with the reference electrodes being connected electrically in parallel to monitor the potential. The reference electrode arrangement serves in this case in the known way to maintain the potential relationships demanded for the treatment process and can be connected to a potentiostat for this purpose for example. The individual electrodes of the reference electrode arrangement connected in parallel behave like resistors connected in parallel, so that the same potential is present at them in each case.

The invention further relates to a counter-electrode arrangement for the electrochemical treatment of workpieces, in which the workpiece forms the working electrode.

This type of counter-electrode arrangement is for example known from EP 1 094 134 A1. This counter-electrode arrangement consists of two electrode plates, which can be directed from both sides onto a turbine blade from which the coating is to be removed. The electrode plates can in this case have surfaces designed in accordance with the profile of the turbine blade. This allows a constant distance to be maintained between the electrode plates and the surface of the turbine blade from which the surface is to be removed.

A further object of the invention is to specify a counter-electrode arrangement for electrochemical treatment processes with which the counter-electrode arrangement can be positioned in a simple manner in relation to a workpiece to be treated.

In accordance with the invention this object is achieved with the counter-electrode arrangement mentioned, by a reference electrode arrangement being mechanically connected to the counter-electrode arrangement, with the connection being embodied as electrical isolation between the counter-electrode arrangement and the reference electrode arrangement and the reference electrode arrangement being embodied from a number of individual electrodes, with electrode tips which are able to be moved within a treatment area provided for the workpiece. By embodying the reference electrode arrangement with a number of individual electrodes featuring electrode tips, a simple alignment of the counter-electrode arrangement can advantageously be undertaken when the counter-electrode is aligned in relation to the workpiece to be treated, since, to achieve a working potential necessary for even treatment between counter-electrode arrangement and workpiece, a comparison potential can be determined by means of the reference electrode arrangement with a local resolution over the surface of the workpiece. The method needed for this has already been explained. The mechanical coupling between counter-electrode arrangement and reference electrode arrangement means that precise geometrical circumstances are advantageously defined between the two electrode arrangements, so that an alignment of the reference electrode arrangement automatically leads to an alignment of the counter-electrode arrangement.

The connection points between counter-electrode arrangement and reference electrode arrangement must be electrically isolated to enable the two electrode systems to be operated independently of one another. The electrically isolating connection can preferably consist of electrically isolating connection elements. These can for example be attached in the counter-electrode arrangement and simultaneously implement a guide for the individual electrodes of the reference electrode arrangement.

In accordance with a further embodiment of the counter-electrode arrangement there is provision for the counter-electrodes of the counter-electrode arrangement to be embodied flat and be able to be deformed within the treatment area. The counter-electrode can for example be designed as a flexible grid. This allows the deformable counter-electrode arrangement to be adapted in the optimum way to the geometry of the workpiece to be treated. In this case the deformability allows an adaptation within a treatment area defined by the limits of the deformability. This enables workpieces to be treated evenly provided their surface to be handled lies within the treatment area.

The individual electrodes of the counter-electrode arrangement can advantageously be embodied in the form of bars and can be fixed axially in the counter-electrode. They can preferably be fixed with the connecting pieces already described. The axial displacement capability of the individual electrodes makes it possible to position the electrode tip with smaller distance to the surface of the workpiece than the distance between the counter-electrode arrangement and the workpiece surface. This is especially of advantage for the generation of measured values in executing the electrochemical treatment method.

It is further advantageous for the individual electrodes to be held to allow axial movement in an electrode carrier. This allows the electrode tips to be adapted to the contour of the workpiece to be treated, so that an even distance between the electrode tip and the workpiece surface is produced. If the deformable flat counter-electrode is attached rigidly to the rod-shaped individual electrodes, displacement of the individual electrodes simultaneously allows the adaptation of the counter-electrode to the contour of the workpiece to be treated. In this case the individual electrodes are advantageously additionally given a support function for the counter-electrode arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of the invention are described below with reference to the drawing. In this case the same elements or corresponding elements in the figures are provided with the same reference symbols, with these only being explained more than once to indicate how differences between the individual figures are produced. The figures show

FIG. 1 an exemplary embodiment of the inventive counter-electrode arrangement in an electrochemical treatment bath for executing exemplary embodiments of the inventive method and

FIG. 2 the structure of an exemplary embodiment of the inventive counter-electrode arrangement as a sectional view.

DETAILED DESCRIPTION OF INVENTION

An electrochemical treatment bath 12 is poured into a container 11. Also fixed in the treatment bath are a workpiece 13 (for example the blades a gas turbine, not shown) and a counter-electrode arrangement 14. The counter-electrode arrangement consists of a flexible, grid-type counter-electrode 15 and a contacting system 16. Furthermore connecting pieces 17 are fixed in the grid, in which bar-shaped individual electrodes 18 are held electrically isolating. These form a reference electrode arrangement 19, with the electrode tips 20 pointing towards but not making contact with the surface to be treated 21 of the workpiece 13, whereas contacting systems 22 are provided at the opposite ends of the individual electrodes 20. The individual electrodes 18 are further aligned in their axial extension at right angles to the surface 21 and also penetrate the counter-electrode 15 at a right angle to their spatial alignment, so that the counter-electrode 15 runs essentially in parallel to the surface 21.

The workpiece 13, the counter-electrode arrangement 14 and the reference electrode arrangement 19 can be connected via electrical lines 23 to a potentiostat 24. The individual electrodes 18 are connected via individual lines 25 with a switching unit 26, via which an electrical connection to the potentiostat 24 is established. The switching unit further features a control and evaluation unit 27. With this the individual electrodes 18 can be switched individually in parallel in respective groups with the aid of the switching unit 26 or switched in parallel in their entirety.

The described arrangement of workpiece 13 (working electrode), counter-electrode arrangement 14 and reference electrode arrangement 19 with potentiostat 24, switching unit 26 and control and evaluation unit 27 allows a number of operating states. In a first operating state a measurement current can be created between the workpiece 13 and the counter-electrode arrangement 14 by means of the potentiostat 24 which is so small that it does not disturb a measurement with the aid of the reference electrode arrangement 19. By means of the individual electrodes 25 a local measurement potential can then be measured which is present between the respective electrode tip and the local, adjoining surface areas of the workpiece 13. The geometry of the counter-electrode 15 is modified until such time as the comparison potential at the individual electrodes 18 is at least largely balanced. The data is processed in this case by the control and evaluation unit 27.

In a next step the desired electrochemical treatment process is undertaken. This can for example consist, for worn turbine blades, of removing the coating and of subsequently recoating the blade, so that the turbine blades can be used again. In this case the individual electrodes in the control unit are switched electrically in parallel and are connected to the potentiostat 24 to maintain constant treatment parameters.

With the counter-electrode arrangement 14 in accordance with FIG. 2 the individual electrodes 20 are axially guided in an electrode carrier 28. To ensure that they are isolated from each other electrically-isolating guide bushes 29 are let into the electrode carriers 28 for this purpose. The figure also shows the connecting pieces 17, which are rigidly attached to the individual electrodes and are connected on their other side to the grid of the counter-electrode 15 (for example through casting) If the individual electrodes are axially displaced in the electrode carrier 28, the counter-electrode 15 thus accordingly matches the axial displacement. The contacting systems 22 are embodied as plug-in connectors (not shown) for the individual lines 25.

The electrode carrier 28 also brings about a parallel alignment between the individual electrodes 18. A constant distance between the electrode tip 20 and a surface (not shown) of the workpiece to be treated means that simultaneously a constant distance between the counter-electrode and this surface is obtained. 

1-5. (canceled)
 6. A method for monitoring an electrochemical treatment process for treatment of a workpiece, comprising: using the workpiece as a working electrode; providing a reference electrode arrangement having a plurality of individual electrodes; moving the individual electrodes in a non-contact manner at a plurality of locations towards a surface of the workpiece to be treated; and maintaining a predetermined potential between the working electrode and a counter-electrode arrangement based upon a reference electrode arrangement.
 7. The method as claimed in claim 6, further comprising: applying a potential, predetermined for the treatment process, to the workpiece and to the counter-electrode arrangement.
 8. The method as claimed in claim 7, further comprising: monitoring the applied potential based upon the reference electrode arrangement, wherein the individual electrodes are switched electrically in parallel.
 9. The method as claimed in claim 8, further comprising: evaluating measurement results of the individual electrodes.
 10. The method as claimed in claim 9, wherein a potentiostat is used for maintaining the predetermined potential between the working electrode and a counter-electrode arrangement.
 11. the method as claimed in claim 10, wherein the measurement results of the individual electrodes are evaluated jointly.
 12. the method as claimed in claim 10, wherein the measurement results of the individual electrodes are evaluated separately.
 13. The method as claimed in claim 6, wherein before the electrochemical treatment a voltage is applied to the workpiece and to the counter-electrode arrangement to create a small measurement current, by comparison with the treatment process, and wherein a comparison potential is determined at the individual electrodes.
 14. The method as claimed in claim 13, wherein the individual electrodes are combined in a group, wherein the determination of the comparison potential is based upon the group.
 15. The method as claimed in claim 13, wherein the comparison potentials are balanced based upon the arrangement of the counter-electrodes in relation to the workpiece.
 16. The method as claimed in claim 6, wherein the potential predetermined for the treatment process is applied to the workpiece and to the counter-electrode arrangement, wherein the reference electrodes are connected electrically in parallel.
 17. A counter-electrode arrangement for the electrochemical treatment of a workpiece, comprising: a working electrode, wherein the workpiece is the working electrode; and a reference electrode arrangement connected mechanically to the counter-electrode arrangement via a connection, wherein the connection is an electrical isolation between the counter-electrode arrangement and the reference electrode arrangement, and wherein the reference electrode arrangement has a number of individual electrodes with electrode tips to be moved within a treatment area of the workpiece.
 18. The counter-electrode arrangement as claimed in claim 17, wherein the counter-electrode is flat and formable within the treatment area.
 19. The counter-electrode arrangement as claimed in claim 18, wherein the individual electrodes are bars and fixed axially in the counter-electrode.
 20. The counter-electrode arrangement as claimed in claim 19, wherein the individual electrodes are held in an electrode carrier, wherein the individual electrodes are axial displaceable.
 21. A method for monitoring an electrochemical treatment process of a blade of a gas turbine, comprising: using the blade as a working electrode; providing a reference electrode arrangement having a plurality of individual electrodes; moving the individual electrodes in a non-contact manner at a plurality of locations towards a surface of the blade to be treated; and maintaining a predetermined potential between the working electrode and a counter-electrode arrangement based upon a reference electrode arrangement.
 22. The method as claimed in claim 21, further comprising applying a potential, predetermined for the treatment process, to the blade and to the counter-electrode arrangement.
 23. The method as claimed in claim 22, further comprising monitoring the applied potential based upon the reference electrode arrangement, wherein the individual electrodes are switched electrically in parallel.
 24. The method as claimed in claim 21, wherein the electrochemical treatment process is a coating process of the blade.
 25. The method as claimed in claim 21, wherein the electrochemical treatment process removes a coating of the blade. 